Methods and apparatus for injecting atomized fluid

ABSTRACT

The present invention provides methods and apparatus for injecting fluid, such as an aqueous urea solution, into an exhaust stream in order to reduce oxides of nitrogen (NOx) emissions from diesel engine exhaust. The present invention uses mechanical spill return atomization techniques to produce droplets having an average size of approximately 50 μm SMD or smaller. This size range is appropriate to allow urea to react into ammonia within the residence time associated with an on-road diesel engine. This effect is achieved through the use of a whirl plate having a plurality of whirl slots surrounding an exit orifice of the injector, which produce a high velocity rotating flow in the whirl chamber. When the rotating flow of fluid is passed through the exit orifice into an exhaust stream, atomization occurs from a combination of centrifugal force and shearing of the fluid by air as it jets into the exhaust stream.

This application is a continuation-in-part of co-pending, commonlyassigned U.S. patent application Ser. No. 11/112,039 filed on Apr. 22,2005, which claims the benefit of U.S. Provisional Application No.60/565,356, filed Apr. 26, 2004.

BACKGROUND OF THE INVENTION

The present invention relates generally to the reduction of emissionsproduced by lean burn engines. In particular, the present inventionprovides methods and apparatus for injecting fluid, such as an aqueousurea solution, into an exhaust stream in order to reduce oxides ofnitrogen (NOx) emissions from diesel engine exhaust.

Lean burn engines provide improved fuel efficiency by operating with anexcess of oxygen over the amount necessary for complete combustion ofthe fuel. Such engines are said to run “lean” or on a “lean mixture.”However, this increase in fuel economy is offset by undesired pollutionemissions, specifically in the form of oxides of nitrogen (NOx).

One method used to reduce NOx emissions from lean burn internalcombustion engines is known as selective catalytic reduction (SCR). SCR,when used, for example, to reduce NOx emissions from a diesel engine,involves injecting an atomized reagent into the exhaust stream of theengine in relation to one or more selected engine operationalparameters, such as exhaust gas temperature, engine rpm or engine loadas measured by engine fuel flow, turbo boost pressure or exhaust NOxmass flow. The reagent/exhaust gas mixture is passed through a reactorcontaining a catalyst, such as, for example, activated carbon, ormetals, such as platinum, vanadium or tungsten, which are capable ofreducing the NOx concentration in the presence of the reagent. An SCRsystem of this type is disclosed in U.S. Pat. No. 5,976,475.

An aqueous urea solution is known to be an effective reagent in SCRsystems for diesel engines. However, use of such an aqueous ureasolution involves many disadvantages. Urea is highly corrosive andattacks mechanical components of the SCR system, such as the injectorsused to inject the urea mixture into the exhaust gas stream. Urea alsotends to solidify upon prolonged exposure to high temperatures, such asencountered in diesel exhaust systems. Solidified urea will accumulatein the narrow passageways and exit orifice openings typically found ininjectors. Solidified urea may foul moving parts of the injector andclog any openings, rendering the injector unusable.

In addition, if the urea mixture is not finely atomized, urea depositswill form in the catalytic reactor, inhibiting the action of thecatalyst and thereby reducing the SCR system effectiveness. Highinjection pressures are one way of minimizing the problem ofinsufficient atomization of the urea mixture. However, high injectionpressures often result in over-penetration of the injector spray plumeinto the exhaust stream, causing the plume to impinge on the innersurface of the exhaust pipe opposite the injector. Over-penetrationleads to inefficient use of the urea mixture and reduces the range overwhich the vehicle can operate with reduced NOx emissions. Only a finiteamount of aqueous urea can be carried on a vehicle, and what is carriedshould be used efficiently to maximize vehicle range and reduce the needfor frequent fill ups of the reagent.

Further, aqueous urea is a poor lubricant. This characteristic adverselyaffects moving parts within the injector and requires that special fits,clearances and tolerances be employed between relatively moving partswithin an injector. Aqueous urea also has a high propensity for leakage.This characteristic adversely affects mating surfaces requiring enhancedsealing resources in many locations.

An example of a prior art injector for injecting aqueous urea into theexhaust stream of a lean bum diesel engine is described in U.S. Pat. No.6,279,603. This prior art injector uses an atomizing hook external tothe injector to cause dispersion of the urea solution expelled from theinjector. The urea solution is circulated in the area of the exitorifice of the injector body to provide cooling.

It would be advantageous to provide methods and apparatus for injectingan aqueous urea solution into the exhaust stream of a lean burn enginewhere atomizing of the urea solution occurs internally to the injectorprior to being injected into the exhaust stream. It would be furtheradvantageous to provide for cooling of the injector to prevent the ureafrom solidifying and to prolong the life of the injector components. Itwould be advantageous to minimize heat transfer to the injector from theexhaust pipe for minimal deposit formation internal to the injector. Itwould also be advantageous to minimize heat transfer from the hot gas tothe exit orifice to prevent soot and urea from being attracted to therelatively cool injector exit orifice, creating deposits external to theinjector. It would also be advantageous to provide an injector that doesnot leak for economical and environmental purposes.

The methods and apparatus of the present invention provide the foregoingand other advantages.

SUMMARY OF THE INVENTION

The present invention provides improved methods and apparatus forinjecting fluid, such as an aqueous urea solution, into an exhauststream in order to reduce oxides of nitrogen (NOx) emissions from dieselengine exhaust. In particular, the injector of the present invention isan enhanced performance atomizer for use with any diesel or natural gasengine.

Current smaller displacement on and off-road diesel engine ureainjectors utilize dual fluid atomization techniques. This processrequires a separate air compressor. Other prior art atomizationtechniques, such as that disclosed in U.S. Pat. No. 6,279,603 ('603patent) utilize an injector which does not have an atomization processinternal to the injector. The injector described in the '603 patentsprays a free jet of liquid that produces small droplets upon impactinga hot plate or hook positioned on the outside of the injector body.

The present invention provides improvements to prior art aqueous ureainjectors, in particular, improvements to an aqueous urea injector ofthe type described in the '603 patent. The present invention utilizesatomization techniques that occur internal to the injector. Inparticular, the present invention uses mechanical spill returnatomization techniques to produce droplets smaller than anticipated bythe inventors, in particular, droplets approximately 50 μm SMD (Sautermean diameter) or smaller. This size range is appropriate to allow ureato react into ammonia within the residence time associated with anon-road diesel engine, unlike the injector described in the '603 patent.This effect is achieved through the use of a whirl plate having aplurality of whirl slots surrounding the exit orifice of the injector,which produce a high velocity rotating flow in the whirl chamber. When aportion of the rotating flow of fluid is passed through the exit orificeinto an exhaust stream, atomization occurs from a combination ofcentrifugal force and shearing of the fluid by air as it jets into theexhaust stream.

In addition, the present invention provides further improvements overthe injector of the '603 patent, including increased magnetic pullstrength of the metering plug over a wide temperature range, prolongedlife of the injector valve and associated actuating components, andcooling with the urea throughout the injector. Additionally, the presentinvention incorporates adjustable spray quality characteristics on line,and interchangeability of orifice plates for multiple size applications.The ribbed injector body provides additional cooling capability.

The present invention may be further adapted to provide an injector forinjecting hydrocarbons particularly for the purposes of regenerating aparticulate filter in a diesel exhaust or for use in a hydrocarbon basedlean-NOx catalyst system. The combination of pulse width modulationproviding instantaneous timing control and mechanical atomizationtechniques is appropriate for providing small quantities of hydrocarbonswith precise timing. The cooling aspects provided by the presentinvention allow the injector to survive the hot exhaust conditions aswell as prevent pre-ignition of the hydrocarbon.

In an example embodiment of the present invention, methods and apparatusfor injecting atomized fluid are provided. An injector is provided,which comprises an injector body, and a whirl chamber arranged on theinjector body. The whirl chamber has an exit orifice. A plurality ofwhirl slots may be provided in the whirl chamber for imparting arotational velocity to fluid introduced into the whirl chamber. A valveseat positioned within the whirl chamber surrounds the exit orifice. Ametering plug may be arranged within the injector body. An actuator mayalso be mounted on the injector body and connected to the metering plugfor moving the metering plug between closed and open positions. Theactuator may be located in the injector body and connected to themetering plug for enabling movement of the metering plug from the closedposition to the open position.

The metering plug may be located in the injector body such that when themetering plug is in a closed position, the metering plug is seated inthe valve seat preventing fluid from being dispensed from the exitorifice. In one example embodiment, the fluid may be circulated throughthe injector to cool the injector when the metering plug is in theclosed position. When the metering plug is in the open position, themetering plug is removed from the valve seat allowing fluid to bedispensed from the exit orifice. In the open position, the end of themetering plug is removed from the valve seat, and a portion of therotating flow of fluid from the whirl chamber is passed through the exitorifice, where atomization occurs from a combination of centrifugalforce and shearing of the fluid by air as it is dispensed into theexhaust stream.

The injector may further comprise a fluid inlet extending into theinjector and a fluid outlet extending out of the injector. The fluidinlet and fluid outlet may communicate with the whirl chamber via ahollow portion of the metering plug. The fluid inlet, the fluid outlet,and the hollow portion of the metering plug may provide a flow path forfluid through the injector, thereby enabling cooling of the injector.The flow path for the fluid through the injector may be providedindependently of the position of the metering plug.

A metering orifice located in the injector body may control the flowrate of cooling fluid flowing through the injector at a given inletpressure. The fluid may be a urea solution or a hydrocarbon.

In a further example embodiment, a plurality of ribs, surrounding theinjector body, may be provided to disperse heat away from the injectorbody. A heat shield, surrounding the exit orifice, may also be providedto decrease the heat transfer from the exhaust stream to the injectorbody. The heat shield may have an aperture therethrough aligned with theexit orifice, thereby allowing fluid released from the whirl chamber topass through the heat shield. The heat shield may comprise a platesurrounding the exit orifice and a layer of insulating material arrangedon the plate.

The injector body and metering plug may comprise stainless steel. Abiasing member may be provided to bias the metering plug into the closedposition, thereby providing a fail-closed valve. The biasing member maybe a coil spring arranged coaxially with the metering plug.

The actuator may comprise a magnetic coil generating a magnetic force.The magnetic force may effect a sliding motion of the metering plugagainst the biasing member when the magnetic coil is energized. Themetering plug may thereby be moved from the closed position to the openposition within the whirl chamber when the actuator is energized,enabling fluid to be dispensed from the exit orifice of the whirlchamber. Means for energizing the magnetic coil may be provided. Forexample, a 12 V pulse width modulated signal may energize the magneticcoil for a definite time period to inject a certain amount of fluid.Other means for energizing the magnetic coil which will be apparent tothose skilled in the art may also be employed.

A method of injecting a fluid into a gas stream is also provided inaccordance with the invention. One example embodiment of such a methodincludes introducing a reagent into an injector body via a fluid inlet,providing a predetermined pressure setpoint for pressurizing the reagentin the injector body, imparting a high velocity rotating flow to atleast a portion of the pressurized reagent within a whirl chamber of theinjector body, and metering a precise amount of atomized reagent from anexit orifice into the exhaust gas stream. The predetermined pressuresetpoint may be variable within a range of approximately 50 to 200pounds per square inch. The whirl chamber may have a plurality of whirlslots. A fluid outlet may be provided for removing any reagent notmetered into the exhaust stream from the injector body.

The fluid in excess of the amount precisely metered may be circulatedthrough the injector body to enable at least one of: (a) maintaining ofthe reagent within a desired temperature range; and (b) maintaining ofthe injector within a desired temperature range. A flow rate of thereagent circulating through the injector body may be variable fromapproximately 2 to 20 gallons per hour. The desired temperature rangefor the reagent may comprise 5° C. to 85° C.

The reagent may comprise a urea solution, a hydrocarbon based reagent,or any other suitable reagent capable of reducing unwanted substancesfrom engine exhaust streams. The exhaust gas stream may comprise adiesel engine exhaust stream or a natural gas or biodiesel engineexhaust stream.

The predetermined pressure setpoint may be variable to provide at leastone of increased operating range and varied spray patterns. Varying thepredetermined pressure setpoint may vary an average droplet size of theatomized reagent metered into the exhaust gas stream. The averagedroplet size may be within a range of approximately 40 to 60 μm SMD.

Varying the predetermined pressure setpoint may also vary a flow rate ofthe atomized reagent metered into the exhaust gas stream. The flow rateof the atomized reagent metered into the exhaust gas stream may bevaried from approximately 0.5 to approximately 700 grams per minute(e.g., by varying at least one of the predetermined pressure, injectoron-time, pulse width modulation frequency of the injector, and exitorifice size). Varying the flow rate further varies at least one of: (1)a droplet size of the atomized reagent metered into the exhaust gasstream; and (2) an amount of cooling provided by circulating reagentremaining in the injector body through the injector body.

The plurality of whirl slots may comprise at least four whirl slots. Thewhirl slots may be arranged transversely to a longitudinal axis of theinjector body. The whirl chamber may be provided in a whirl plate, whichmay be removable from the injector body. Thus, different whirl plateswith correspondingly different characteristics can be interchanged inthe injector body for different applications of the injector (e.g.,different whirl plates to provide certain performance characteristicsfor passenger cars, light duty trucks, heavy duty trucks, generators,and the like). The different whirl plates may provide different spraypatterns of the atomized reagent metered into the exhaust gas stream.Further, the different characteristics of the different whirl plates maycomprise at least one of a different number of whirl slots, whirl slotsof different length, whirl slots of different width, whirl slots ofdifferent depth, a differently sized whirl chamber, a differently sizedexit orifice, and the like.

In addition, a metering plug may be arranged within a lower section ofthe injector body. The metering of the reagent into the exhaust gasstream may be controlled via movement of the metering plug from betweenan open position opening the exit orifice and a closed position closingthe exit orifice.

A flow path may be provided for the reagent through the injector body.The flow path may comprise a fluid inlet arranged in the lower sectionof the injector body, a hollow portion extending through the meteringplug, and a fluid outlet in an upper section of the injector body. Thereagent may be continuously circulated through the flow path, therebyenabling continuous cooling of the injector in both the open and closedposition of the metering plug.

The fluid inlet may be proximate the whirl chamber in a lower portion ofthe injector body and the fluid outlet may be positioned in a topportion of the injector body. Cooling of the injector tip (e.g., in theregion of the valve seat) is of great importance to preventsolidification of the reagent in this area, which can result in cloggingof the injector. By positioning the fluid inlet adjacent the whirlchamber in the lower portion of the injector body, cooling at theinjector tip is maximized since the fluid is not significantly heated bytraveling through the injector body.

Apparatus providing means to accomplish the methods described herein arealso provided in accordance with the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction withthe appended drawing figures, wherein like numbers denote like elements,and:

FIG. 1 shows a schematic diagram of an example embodiment of an on-roaddiesel engine with a pollution emission control system using an injectoraccording to the present invention;

FIG. 2 shows a longitudinal cross-sectional view of an exampleembodiment of an injector according to the invention;

FIG. 3 (FIGS. 3A, 3B, and 3C) shows top, cross-sectional, and bottomviews of an example embodiment of a whirl plate in accordance with thepresent invention;

FIG. 4 (FIGS. 4A and 4B) shows an example embodiment of a metering plugused in the injector of FIG. 2; and

FIG. 5 shows a perspective view of an example embodiment of an injectormounted on an exhaust tube in accordance with the present invention.

DETAILED DESCRIPTION

The ensuing detailed description provides exemplary embodiments only,and is not intended to limit the scope, applicability, or configurationof the invention. Rather, the ensuing detailed description of theexemplary embodiments will provide those skilled in the art with anenabling description for implementing an example embodiment of theinvention. It should be understood that various changes may be made inthe function and arrangement of elements without departing from thespirit and scope of the invention as set forth in the appended claims.

FIG. 1 shows an example pollution control system for reducing NOxemissions from the exhaust of a diesel engine 21. In FIG. 1, solid linesbetween the elements of the system denote fluid lines and dashed linesdenote electrical connections. The system of the present invention mayinclude reagent tank 10 for holding the reagent (e.g., aqueous urea) anda delivery module 12 for delivering the reagent from the tank 10. Thetank 10 and delivery module 12 may form an integrated reagenttank/delivery module. Also provided as part of the system is anelectronic injection control unit 14, an injector module 16, and anexhaust system 19 having at least one catalyst bed 17.

The delivery module 12 may comprise a pump that is supplied reagent fromthe tank 10 through an in-line filter 23 via a supply line 9. Thereagent tank 10 may be polypropylene, epoxy coated carbon steel, PVC, orstainless steel and sized according to the application (e.g., vehiclesize, intended use of the vehicle, and the like). The filter 23 mayinclude a housing constructed of rigid plastic or stainless steel with aremovable cartridge. A pressure regulator (not shown) may be provided tomaintain the system at predetermined pressure setpoint (e.g.,approximately 50-200 psi) and may be located in the return line 35 fromthe injector 16. A pressure sensor may be provided in the flexible lineleading to the reagent injector 16. The system may also incorporatevarious freeze protection strategies to unthaw frozen urea or to preventthe urea from freezing. For example, during system operation, regardlessof whether or not the injector is releasing reagent into the exhaustgases, reagent is circulated continuously between the tank 10 and theinjector 16 to cool the injector and minimize the dwell time of thereagent in the injector so that the reagent remains cool. Continuousreagent circulation is necessary for temperature-sensitive reagents,such as aqueous urea, which tend to solidify upon exposure to elevatedtemperatures of 300° C. to 650° C. as would be experienced in an engineexhaust system. It has been found to be important to keep the ureamixture below 140° C. and preferably in a lower operating range between5° C. and 95° C. to provide a margin of safety ensuring thatsolidification of the urea is prevented. Solidified urea, if allowed toform, would foul the moving parts and openings of the injector,eventually rendering the injector useless. It will be recognized thatflow rates will depend on engine size and NOx levels.

The amount of reagent required may vary with load, engine RPM, enginespeed, exhaust gas temperature, exhaust gas flow, engine fuel injectiontiming, and desired NOx reduction. All or some of the engine operatingparameters may be supplied from the engine control unit 27 via theengine/vehicle databus to the reagent injection controller 14. Thereagent injection control unit 14 could also be included as part of theengine control unit 27 if the truck manufacturer agrees to provide thatfunctionality.

Exhaust gas temperature, exhaust gas flow and exhaust back pressure maybe measured by respective sensors.

A minimum reagent level switch or programmed logic based on voltage maybe used to prevent the injection system from running dry andoverheating. Once a minimum reagent level in the tank 10 is reached,injection will cease and a fault light and/or a text alarm willilluminate in the cab of the vehicle.

The injection rate may be set by programming the reagent injectioncontrol unit 14 with an injection control strategy or map, as describedin commonly owned co-pending U.S. Pat. No. 6,941,746 issued on Sep. 13,2005 entitled “Mobile Diesel Selective Catalytic Reduction Systems andMethods” which is incorporated herein and made a part hereof byreference. As described therein, the injection strategy may be developedby temporarily installing a NOx detector 25 on the vehicle. The NOxdetector 25 may be a sensor or a meter with a sampling system. FIG. 1shows a NOx meter 25 which analyzes the gas concentration or mass at alocation external to the exhaust system 19.

FIG. 2 shows a cross-sectional view of an example embodiment of theinjector 16 according to the present invention, which may be used in thesystem shown in FIG. 1. Injector 16 may comprise an injector body 18having an upper section 18 a and a lower section 18 b. An elongatedcylindrical chamber 30 may be disposed within the injector body 18. Thechamber 30 may be in fluid communication with a whirl plate 50, whichhas an exit orifice 22 that opens onto the exhaust gases within theexhaust system 19 (FIG. 1) of a diesel engine when mounted thereon.Surrounding exit orifice 22 may be a valve seat 24 which can have anypractical shape but is preferably conical. A valve member in the form ofan elongated metering plug 26 may be slidably mounted within the chamber30.

FIG. 3A shows a top view of the whirl plate 50. FIG. 3B shows across-sectional view of the whirl plate 50. FIG. 3C shows a bottom viewof the whirl plate 50. As can be seen from FIG. 3A, the whirl plate 50may include a plurality of whirl slots 51 surrounding the valve seat 24and forming a whirl chamber 52 in the area surrounding the end 28 of themetering plug 26 (see FIG. 2). The whirl slots 51 may be arrangedtransversely to a longitudinal axis of the injector body 18, as shown inFIG. 3A. As can be seen from FIGS. 3A and 3B, the valve seat 24surrounds the exit orifice 22 for dispensing the atomized fluid from thewhirl chamber 52. The whirl plate 50 may be affixed to the lower sectionof the injector body 18 b by a retaining cap 74.

In the example configuration shown, a fluid-retaining gasket 60 may beinterposed between the whirl plate 50 and the lower portion of theinjector body 18 b to prevent fluid from leaking between the matingsurfaces of the whirl plate 50, injector body 18 and retaining cap 74.The gasket may comprise a silicone material. The upper injector body 18a may include several sealing O-Rings 76 interposed between matingsurfaces of the upper injector body 18 a and lower injector body 18 b,lower injector body 18 b and bottom plate 75, bottom plate 75 and coil38, and coil 38 and upper injector body 18 a to prevent fluid leaks.

FIGS. 4A and 4B show cross-section and exterior views, respectively, ofan example embodiment of metering plug 26. Metering plug 26 may have anend 28 formed to sealingly engage valve seat 24, thereby closing exitorifice 22 from fluid communication with the whirl chamber 52. Meteringplug 26 may be movable within the whirl chamber 52 between the closedposition shown in FIG. 2 and an open position wherein end 28 is removedfrom sealing engagement with valve seat 24. In the open position, exitorifice 22 is opened to fluid communication with the whirl chamber 52.

Fluid may be delivered to the whirl chamber 52 via a fluid inlet 34(FIG. 2). Fluid inlet 34 may be in fluid communication with the whirlchamber 52 and may be externally connected to tank 10 via supply line 9.Fluid, such as aqueous urea reagent, may be pumped at a predeterminedpressure setpoint into the fluid inlet 34 and into the whirl chamber 52.The pressurized fluid may be accelerated to high velocity in the whirlslots 51. This produces a high velocity rotating flow in the whirlchamber 52. When the end 28 of the metering plug is removed from thevalve seat 24, a portion of the rotating flow of fluid is passed throughexit orifice 22, where atomization occurs from a combination ofcentrifugal force and shearing of the fluid by air as it jets into theexhaust stream.

The predetermined pressure setpoint may vary in response to operatingconditions to provide at least one of increased operating range andvaried spray patterns from the exit orifice 22. For example, thepredetermined pressure setpoint may be varied between approximately50-200 psi, and for optimum results between approximately 60-150 psi.

To effect the opening and closing of the exit orifice 22, an actuatormay be provided, for example in the form of magnetic coil 38 mounted inthe injector body 18. When the magnet 38 is energized, the metering plug26 is drawn upward from the closed position to the open position. Thebottom plate 75 and the upper injector body 18 a may be constructed ofmagnetic stainless steel to provide a magnetized surface while retainingthe corrosion resistant characteristics. The bottom injector body 18 bmay be constructed of a non-magnetic stainless steel such as type 316stainless steel. This enhances the isolation of the magneticcharacteristic at the bottom plate 75 and limits the potential for themetering plug 26 to be magnetized toward the exit orifice 22. The magnetwould be energized, for example, in response to a signal from electroniccontroller 14 of FIG. 1, which decides, based upon sensor input signalsand its preprogrammed algorithms, when reagent is needed for effectiveselective catalytic reduction of NOx emissions in the exhaust stream.

FIG. 5 shows an external view of the injector 16 connected to an exhausttube 80. Electrical connections 82 may be provided for providing acontrol signal to the injector 16, for example from the reagentinjection controller 14 (FIG. 1). The magnetic coil 38 may be energizedby a 12-24 VDC current with a pulse width modulated digital signal.

As shown in FIG. 4A, the metering plug 26 includes a hollow section 90which may be in fluid communication with the whirl chamber 52 via bores92 in the metering plug 26. The pressurized fluid from the whirl chamber52 which is not expelled from exit orifice 22 may be forced into bores92, into the hollow section 90 and ultimately into outlet 36 through thehollow top portion 94 of the metering plug 26. The fluid outlet 36 maybe positioned as shown in FIG. 2 for removing fluid from the top portion94 of the hollow section 90 of metering plug 26. Fluid outlet 36 may beexternally connected to return line 35 (FIG. 5), thus permitting thefluid to circulate from the tank 10 of FIG. 1, through supply line 9,through fluid inlet 34, into the whirl chamber 52, through bores 92,through the hollow section 90 of metering plug 26, out of hollow topportion 94 and into fluid outlet 36, through return line 35 and backinto tank 10 of FIG. 1. This circulation keeps the injector 16 cool andminimizes the dwell time of the fluid in the injector. The fluid inlet34, fluid outlet 36, and the hollow portion 90 of the metering plug 26may provide a flow path for fluid flowing through the injector 16,thereby enabling cooling of the injector 16. The flow path for fluidthrough the injector 16 may be independent of the position of themetering plug 18. A metering orifice 37 may be provided for controllingthe amount of cooling fluid flowing through the injector 16.

The fluid inlet 34 may be proximate the whirl chamber 52 in a lowerportion of the injector body 18 b and the fluid outlet 36 may bepositioned in a top portion of the injector body, as shown in FIG. 1.Cooling of the injector tip (e.g., in the region of the valve seat 24)is of great importance to prevent solidification of the reagent in thisarea, which can result in clogging of the injector 16. By positioningthe fluid inlet 34 adjacent the whirl chamber in the lower portion ofthe injector body 18 b, cooling at the injector tip is maximized sincethe fluid is not significantly heated by traveling through the injectorbody 16. Thus, for example, aqueous urea, when used with this cooledinjector 16, will not solidify anywhere within the injector 16, and inparticular in the area of the whirl chamber 52. If allowed to solidify,the urea could prevent metering plug 26 from seating properly or couldcause the metering plug 26 to seize in either the open or closedposition and/or the exit orifice 22 could become clogged. In addition,the detrimental effects of elevated temperature on the reagent, themoving parts, and the openings of the valve are avoided. In addition, byproviding a cooling path through the entire length of the injector body,including directly cooling the injector tip in the region of the valveseat 24, increased performance is achieved in comparison with the priorart, which provides only limited cooling of the injector. Further, theincreased cooling of the injector body in accordance with the presentinvention provides for prolonged life of the injector components,including the metering plug 26 and associated actuating components, andthe valve seat 24. Cooling ribs 72 provided on the exterior of the upperportion of the injector body 18 a provide additional cooling capacity.

As an example, approximately 10 gallons of fluid may be circulatedthrough the injector per hour. This flow rate may be varied depending onthe application. For example, this flow rate may be varied fromapproximately 2 gallons per hour to approximately 20 gallons per hour.Upon removing the end 28 of the metering plug 26 from the valve seat 24,atomized fluid may be expelled at the rate of approximately 0.5-700grams per minute, depending on the application and/or the controlalgorithm used, as well as the pressure setting and/or the size of theexit orifice 22. The spray characteristics of fluid expelled from theexit orifice 22 may be varied depending on the pressure ratios of thepressure maintained in the return and supply lines. For example, thesize of the droplets may be controlled by varying the pressure in thesupply line 9. In addition, the spray characteristics may be varied byinterchanging different whirl plates. For example, the whirl plate 50,which is affixed to the injector body by retaining cap 74, may beremoved and replaced with whirl plates with different sized exitorifices 22, a different number of whirl slots 51, or whirl slots ofdifferent length, depth or width. Further, different whirl plates may beconfigured to provide larger or smaller whirl chambers 52 when affixedto lower section of the injector body 18 a. The fluid circulation ratecan also be varied by modifying the internal diameter of meteringorifice 37. Varying the fluid circulation rate changes the droplet sizeand impacts the level of cooling provided by the fluid.

Flow of the injector 16 can be varied for higher turndown (i.e., theratio of maximum flow to minimum flow) from a given orifice diameter bychanges in injector pulse-width modulation frequency, injector on-timeand pressure setting. The pressure setting can be varied by any meansincluding operation of a variable speed pump. This feature isparticularly advantageous for exhaust gas treatment systems where a widerange of reagent flows may be needed based not only on engine operationbut also on the condition of aftertreatment hardware such as traps orcatalysts. Varying reagent pressure in the injector body between 80-120psi has unexpectedly been found to provide turndown ratios in the rangeof approximately 5:1 and 50:1 when combined with changes in operatingfrequency and on-time of the injector 16. Pressures of approximately150-200 psi and as low as approximately 50-60 psi can also be used. Forexample, in laboratory flow testing of one embodiment of the injector 16of the present invention having an exit orifice 22 with a 0.030″diameter, a flow range of 12.6 gr/min to 517 gr/min was achieved byvarying on-time from 1% to a maximum, with frequencies of 1.5 Hz to 10Hz and operating pressure of 80 psi using a simulated hydrocarbonreagent marketed under the trade name of Viscor. Boosting the pumppressure to 120 psi increased the maximum flow rate to 631.0 gr/min at afrequency of 10 Hz and maximum injector on-time. A simple increase involtage to the pump was used to adjust pump speed and consequentlyincrease pressure of the reagent in the injector. The system was alsooperated at a steady pressure of 120 psi while varying frequency from1.5 Hz to 10 Hz and injector on-time from 1% to a maximum, resulting ina flow range of 15.1 gr/min to 631 gr/min. Lower flows can beaccomplished by selection of a smaller size for the exit orifice 22. Useof the injector 16 of the present invention with an aqueous solution of32.5% urea will generally provide flows at least 20% greater than thatachieved with the simulated hydrocarbon reagent discussed above, due todensity and viscosity differences between the urea reagent and thehydrocarbon reagent.

A circular guide section 32 of the metering plug 26 may provide the mainguiding function for sliding motion of the metering plug 26 within thechamber 30. The tolerance between the circular guide section 32 and thechamber 30 is sufficient to allow relative motion and lubrication of themetering plug 26 while still guiding the metering plug's motion.

Generally the specific tolerances required at the various sectionsbetween the metering plug 26 and the chamber 30 will vary according tothe operating temperature, operating pressure, the desired flow rate andcirculation rate of the reagent, the tribological properties of thereagent and the materials chosen for the metering plug 26 and injectorbody 18. The tolerances for optimum injector performance may be obtainedexperimentally through field trials.

As seen in FIG. 2, metering plug 26 may be biased in the closed positionby a biasing member, which may be, for example, in the form of a coilspring 42 coaxially arranged with the hollow top portion 94 of themetering plug 26, which serves as a spring seat against which the spring42 can push to bias the metering plug 26.

In the configuration shown, a thermal shield 58 may be mountedexternally to the whirl plate 50 and retaining cap 74 prevents heat fromthe exhaust gases from being transferred to the whirl plate 50 andinjector body 18 while simultaneously providing a heated surfaceensuring that droplets unintentionally contacting the injector body donot form deposits. For example, the thermal shield 58 may be made ofinconel. Alternatively, the exit orifice 22 may be moved to the outsideor injecting end of the whirl plate 50, thereby increasing spray angle αand also allowing a wider range of spray angles while retaining thecooling properties. Thermal gasket 70 may be made of a flexible graphitefoil sheathed in stainless steel material whose low thermal conductivityserves to isolate injector body 18 and the whirl plate 50 from the hotexhaust tube 80, reducing conductive heat transfer to the injector 16and thereby helping to keep the fluid circulating within the valve cool.

The metering plug 26 may be made of type 430C or 440F stainless steelpreferably coated with a coating that retains the urea corrosionresistance and the magnetic properties while reducing the metal fatiguecaused over the life of the injector. The whirl plate 50 may be made ofinconel or type 316 stainless steel and coated with a coating thatretains the urea corrosion resistance while reducing the metal fatiguecaused over the life of the injector 16. The bottom plate 75 may beseparated from the metering plug 26 and the metering plug 26 may beshortened to the shortest length reasonable for manufacturing to providea significantly reduced metering plug mass. The decreased mass of themetering plug 26 prolongs the life of the plug, and in particularprolongs the life of the end 28 of the metering plug, which is subjectto wear and deformation from repeated impact on the valve seat 24.

It should now be appreciated that the present invention providesadvantageous methods and apparatus for injecting an aqueous ureasolution into the exhaust stream on an on-road diesel engine in order toreduce NOx emissions. Although the present invention is described abovein connection with reducing NOx emissions in a diesel engine exhauststream, the present invention is equally applicable to reducing NOxemissions in a natural gas or biodiesel engine exhaust stream.

Although the invention has been described in connection with variousillustrated embodiments, numerous modifications and adaptations may bemade thereto without departing from the spirit and scope of theinvention as set forth in the claims.

1. A method of injecting atomized reagent into an exhaust gas stream atlow pressure, comprising: introducing a reagent into an injector body;providing a predetermined pressure setpoint for pressurizing saidreagent in said injector body, said predetermined pressure setpointbeing variable within a range of approximately 50 to 200 pounds persquare inch; imparting a high velocity rotating flow to at least aportion of the pressurized reagent within a whirl chamber of saidinjector body, said whirl chamber having a plurality of whirl slots; andmetering a precise amount of atomized reagent from an exit orifice intosaid exhaust gas stream.
 2. A method in accordance with claim 1,furthering comprising: circulating reagent maintained in said injectorbody through said injector body to enable at least one of: (a)maintaining of said reagent within a desired temperature range; and (b)maintaining of said injector within a desired temperature range.
 3. Amethod in accordance with claim 2, wherein a flow rate of said reagentcirculating through said injector body is variable from approximately 2to 20 gallons per hour
 4. A method in accordance with claim 2, whereinsaid desired temperature range for said reagent comprises 5° C. to 85°C.
 5. A method in accordance with claim 1, wherein the reagent comprisesa urea solution.
 6. A method in accordance with claim 1, wherein saidreagent comprises a hydrocarbon.
 7. A method in accordance with claim 1,wherein said exhaust gas stream comprises one of a diesel engine exhauststream, a natural gas engine exhaust stream, and a biodiesel engineexhaust stream.
 8. A method in accordance with claim 1, wherein saidpredetermined pressure setpoint is variable to provide at least one ofincreased operating range and varied spray patterns.
 9. A method inaccordance with claim 1, wherein varying said predetermined pressuresetpoint varies an average droplet size of said atomized reagent meteredinto said exhaust gas stream.
 10. A method in accordance with claim 9,wherein said average droplet size is within a range of approximately 40to 60 μm SMD.
 11. A method in accordance with claim 1, wherein varyingsaid predetermined pressure setpoint varies a flow rate of said atomizedreagent metered into said exhaust gas stream.
 12. A method in accordancewith claim 11, wherein said flow rate of said atomized reagent meteredinto said exhaust gas stream is in a range of approximately 0.5 to 700grams per minute.
 13. A method in accordance with claim 11, whereinvarying the flow rate further varies at least one of: (1) a droplet sizeof said atomized reagent metered into said exhaust gas stream; and (2)an amount of cooling provided by circulating reagent remaining in theinjector body through the injector body.
 14. A method in accordance withclaim 1, wherein said plurality of whirl slots comprises at least fourwhirl slots.
 15. A method in accordance with claim 1, wherein: saidwhirl chamber is provided in a whirl plate; and said whirl plate isremovable from said injector body.
 16. A method in accordance with claim15, wherein different whirl plates with correspondingly differentcharacteristics can be interchanged in said injector body for differentapplications of said injector.
 17. A method in accordance with claim 16,wherein said different whirl plates provide different spray patterns ofsaid atomized reagent metered into said exhaust gas stream.
 18. A methodin accordance with claim 16, wherein said different characteristics ofsaid different whirl plates comprise at least one of a different numberof whirl slots, whirl slots of different length, whirl slots ofdifferent width, whirl slots of different depth, a differently sizedwhirl chamber, and a differently sized exit orifice.
 19. A method inaccordance with claim 1, further comprising: providing a metering plugarranged within a lower section of said injector body; and controllingthe metering of said reagent into said exhaust gas stream via movementof the metering plug from between an open position opening said exitorifice and a closed position closing said exit orifice.
 20. A method inaccordance with claim 19, further comprising: providing a flow path forsaid reagent through the injector body, said flow path comprising afluid inlet arranged in the lower section of said injector body, ahollow portion extending through said metering plug, and a fluid outletin an upper section of said injector body; and continuously circulatingsaid reagent through said flow path, thereby enabling continuous coolingof said injector in both the open and closed position of said meteringplug.
 21. A method in accordance with claim 20, wherein the fluid inletis proximate the whirl chamber.
 22. A method in accordance with claim 1,wherein the whirl slots are arranged transversely to a longitudinal axisof said injector body.
 23. A method in accordance with claim 1, whereina flow rate of said atomized reagent metered into said exhaust gasstream can be varied to provide turndown ratios of maximum flow tominimum flow for a specific exit orifice size in the range ofapproximately 5:1 to 50:1 by varying at least one of said predeterminedpressure, a pulse-width modulation frequency of said injector, andinjector on-time.
 24. An atomizing injector comprising: a fluid inletfor introducing a reagent into an injector body; a fluid outlet forremoving the reagent from said injector body; means for providing apredetermined pressure setpoint for pressurizing said reagent in saidinjector body, said predetermined pressure setpoint being variablewithin a range of approximately 50 to 200 pounds per square inch; awhirl chamber for imparting a high velocity rotating flow to at least aportion of said pressurized reagent, said whirl chamber having aplurality of whirl slots; and a metering plug for metering a preciseamount of atomized reagent from an exit orifice into an exhaust gasstream.